Generally, a bumper for a vehicle needs performance of absorbing an impact while a front or rear of a back panel is colliding to ensure the safety of a rider and reduce a damage of the back panel. Among components of such bumper, a bumper beam assembly performs most important role, the bumper beam assembly includes a bumper beam and a crash box; stay.
A bumper needs to satisfy regulations of a low-speed crash test and articles of a research council for automobile repairs (RCAR) test (hereinafter, referred to as the RCAR test), which are semi-regulations, in which, since performances needed in the RCAR test are stricter than the low-speed crash test, when satisfying the needs, it is understood to naturally satisfy the regulations of the low-speed test.
In a general RCAR test, a low-speed crash test (hereinafter, referred to as an offset test; and refer to FIGS. 1A and 1B) is executed at a speed of 15 km/h with a degree of 10° toward a wall offset by 40% and the performance of a bumper is measured by calculating a repair cost for a damage of a back panel and determining an insurance grade. The performance needed in the offset test is replacing only the bumper with no damage of the back panel. A crash box 200 satisfying the performance needed in the offset test is generally formed in a shape shown in FIG. 2A, and a configuration of a bumper beam assembly 200′ using the same is as shown in FIG. 2B. That is, a configuration capable of absorbing impact energy as much as possible by using compression and deformation within a limit that a bumper beam 150 endures to reduce the damage of the back panel in a collision includes a front plate member 210, a rear plate member 220, an outer support member 230, and an inner support member 240 and reduces the damage of the back panel by absorbing the impact energy by using compression and deformation of the outer and inner support members 230 and 240 in a collision as shown in FIG. 3.
However, in a recently changed RCAR test, in addition to the traditional offset test, a low-speed crash test (hereinafter, referred to as a barrier test; and refer to FIGS. 4A and 4B) is executed on a front and a rear of a vehicle at a speed of 10 km/h with a bumper dummy barrier whose height is 18 inches. The performance needed in the barrier test is being with no damage of a back panel and with no occurrence of under ride and over ride. That is, to satisfy the needs of the barrier test, a crash box and a bumper beam maintain suitable strength and reduce deformation to prevent the damage of the back panel.
It is difficult to satisfy the performances needed in the offset test and barrier test of the changed RCAR test, contrary to each other, as described above, which is more difficult in reality in which a limitation is in weight and a cost price and fuel efficiency need to be considered.
Hereupon, to increase the strength of a configuration of the crash box 200 of FIG. 2A, there is disclosed a crash box 300 as shown in FIG. 5A. That is, to satisfy the performance needed in the barrier test, a front part of the inner support member 340 is broaden to a center part of the bumper beam 150 in such a way that strength is increased to prevent a damage of a back panel 170 in a collision (refer to FIG. 5B). However, as shown in FIG. 17, when executing the offset test, the back panel 170 is largely damaged. To satisfy the performances needed in the contrary tests, the shape of the crash box 300 is changed with the inner support member 340 being broaden and a disadvantageous condition such as a weight increase, which causes a decrease in performance thereof.
Accordingly, a shape of a crash box to satisfy the performances needed in the contrary tests is necessary.